For many decades artificial joints and joint prostheses have been used surgically, for example, hip joint prostheses, shoulder prostheses or knee prostheses. The hip joint prosthesis is thus the most commonly performed joint replacement surgery. In Germany alone, approx. 200,000 hip joint endoprostheses are implanted each year. Each year, more than 175,000 people have surgery on their knees due to wear on the joint. However, the stability of these prostheses is limited and therefore they must be replaced after a certain amount of time, in particular due to aseptic loosening of the implants. In the case of a hip joint prosthesis, the service life today is 10-15 years, for example. The incidence of revision surgery in the first ten years after implantation is 10%.
Nevertheless, even a loosened prosthesis or prosthetic part will usually still be very securely attached to and enmeshed with the respective bone structures. Therefore there are still problems in removing a prosthesis from the body without causing sequelae to the surrounding bone bed and/or the patient's other tissues. Conditions are also similar when introducing new prostheses. Furthermore, it is advantageous for the patient to perform the procedure in the manner that conserves as much of the surrounding tissue as possible, so that minimally invasive surgical procedures (MIS) with the smallest possible opening of or injury to the skin and surrounding tissue would be desirable and in the meantime have become quite conventional. Positive effects include the preservation of muscle attachments, preservation of muscle functions, reduced postoperative pain symptoms and faster rehabilitation of the patient. However, this also makes high new demands of the instruments used in minimally invasive insertion and removal of prostheses.
The forces in knocking out a prosthesis must thus be high enough but at the same time they must be transferred in a very targeted manner so that they act only on the shaft/neck of the prosthesis. A very high momentum is necessary to release the bond between the prosthesis and the bony tissue before the energy can be transferred to the bone. This requires an axial transfer force with accurate positioning of the tools as much as possible.
Previous knockout tools can often be used only for one type of prosthesis and in some cases only for prostheses of a specific design and/or a certain manufacturer. Furthermore, the positioning and fixation of the tool are not simple to achieve, as explained above.